1. Field of the Invention
The present invention relates to a silicon-based substrate, a semiconductor device, and a method for manufacturing a semiconductor device, and more particularly to a silicon-based substrate on which a nitride compound semiconductor layer is formed, a semiconductor device using this silicon-based substrate, and a method for manufacturing this semiconductor device.
2. Description of the Related Art
A nitride compound semiconductor layer is generally formed on an inexpensive silicon substrate or a sapphire substrate, but slips or defects are introduced into the silicon substrate by stress applied to the silicon substrate in a process of thickly growing a group III nitride semiconductor layer on the silicon substrate. Consequently, there occurs a problem that a warpage of the fabricated substrate is not stabilized due to these slips or defects.
As means for solving this problem of the warpage of the substrate, there is a method for increasing a thickness of the silicon substrate. However, a thickness of a generally fabricable substrate is approximately 1 mm. Fabrication of a substrate having a larger thickness is difficult due to limitations of an device, a jig, or the like used in a fabrication process of the substrate or a manufacturing line for fabricating a device.
As another means, enhancing strength of the silicon substrate can be considered. As this method, there has been reported that the strength of the silicon substrate is enhanced by setting boron concentration in the silicon substrate to, e.g., 1×1019 atoms/cm3 or more (see Patent Literature 1).
Further, Patent Literature 2 discloses that a warpage of a silicon substrate is reduced by controlling oxygen concentration in the silicon substrate.